The present invention relates to an electrostatic image developer production apparatus suitable for the production of an electrostatic image developer carrier.
The two component developer consisting of a toner and a carrier is advantageous in that the electrification characteristic and the electrification amount of the toner can be controlled to a considerable extent and that the colors to be given to the toner can be selected from a relatively wide range of colors.
For the carrier to be used in the two component developer, a coating carrier consisting of the core materials whose surfaces are covered with the coating resin for the higher durability and the improvement in the triboelectrification characteristic.
The production apparatus of the coating carrier, the fluid layer type apparatus, immersion type apparatus and sintering type apparatus are commonly known, but the fluid layer type apparatus is most widely used because of its high productivity.
The fluid layer type apparatus, however, has the drawbacks such as the high manufacturing cost due to the necessity of the affiliated devices such as the solvent recovery device to recover the waste solvent and the solvent burner and the safety problem due to using the inflammable solvent. In addition, the fluid layer type spray coating method has a certain limit in improving its productivity. For instance, increasing the number of sprays and the spray rate to increase the supply of the coating solution per unit time for higher productivity causes the gasification of the solution present among the core materials to be retarded to cause the solution to turn into the particles of unnecessarily large particle size. On the other hand, increasing the concentration of the solution results in the increase in the viscosity of the solution, which also causes the formation of the solution particles. Besides, in this method, it is essential for the coating resin to be dissolved into the solvent, so that the kinds of the usable resins are limited in terms of their molecular weights. Another drawback of this method is that it is difficult for the cores of the carrier to form the appropriate fluid layer because of their small individual masses resulting from their quite small particle size for realizing high-quality image and high developing efficiency, which results in poor coating efficiency.
Thus, there has been an increasing demand for the development of a new method, and recently, a dry method characterized by applying the impact on the resin particles to cause the particles to adhere to the cores has been developed.
The dry coating method has the following advantages:
(1) The cleansing and drying processes can be eliminated to substantially shorten the time required for coating. PA0 (2) The granulating rate of the solution is relatively small, so that the carrier with the distribution corresponding to the cores which are provided in the form of the magnetic particles can be obtained as a high yield rate. PA0 (3) Unnecessitating the solvent recovery device and the solvent burner, both the reduction of the manufacturing cost and higher safety can be realized. PA0 (4) The quantitative ratio of the resin particles to the magnetic particles in the production apparatus can be reduced for using the materials with higher economy. PA0 (5) The magnetic particles are extended with resin particles adhered to the surfaces of the magnetic particles, so that the hard-to-remove coating films can be formed to obtain high durability and stable triboelectrification characteristic. PA0 (6) Permitting the use of the resins with relatively low solubility to the solvent, not only the resins can be selected within a much wider range but also the coating even with the fine particulate carrier can be made easily to obtain the coating carriers with different characteristics.
The dry coating device not using the solvent can roughly be classified into one using the heat to effect the fused bonding and the other using the mechanochemical effect.
As the examples of the former device, there are the furnace type device introduced in the Japanese patent laid open publication 118047/1980 and the Japanese patent publication 163544/1980, and the rotary furnace type device introduced in the Japanese patent laid open publication 170865/1985 and the Japanese patent publication 106475/1987. Another method of fused bonding using the high-speed stirrer to effect the bonding of the resin particles is disclosed in the Japanese patent laid open publication 27858/1988, through the construction of the device is not described in detail.
In the fused bonding methods using the heater, the temperature of the coating resin is raised above the softening or melting point, so that the cores of the carrier are bonded to each other through the resin which serves as the binder, and this causes the granulating effect due to the increase in the particle size. When the particle size becomes too large, the effect of the developing agent in the developing device becomes uneven to adversely affect the formation of the uniform and high-quality image.
Also, when the carrier obtained by breaking up the granulated carrier is not uniform in coating, thereby causing the unevenness in the triboelectrification characteristic of the toner and the resulting defect of the image such as the fog or the scattering of the toner. Furthermore, this method requires the processing at a high temperature, which poses the safety problem.
On the other hand, as the examples of the latter device, there is one disclosed in the Japanese patent laid open publication 235962/1988, wherein the impact is given by a rotary body disposed in vertical direction to circulate the carrier by moving the carrier upward, and, in this process, unnecessarily large impact is given to the carrier. Thus, when the sintered carrier such as the ferrite carrier is used, the carrier tends to develop the internal cracks to reduce the durability of the carrier.
If the carrier with internal cracks is used, the carrier will be broken up gradually as it is stirred in the developing device, and, as a result, the surfaces of the carriers not covered with the resin coating will be increased. Since the triboelectrification characteristic of the uncoated surfaces of the carrier differs from that of the surface of the carrier with resin coating, the triboelectrification characteristic of the toner will become unstable to deteriorate the image quality. Besides, the broken up particles have smaller particle sizes than the normal particles, so that the holding strength of smaller particles to the sleeve surface are weaker than those of the normal particles, and the smaller particles tend to move onto the photosensitive body (the electrostatic image holding body). As a result, the particles cause the deterioration of the image quality due to the adhesion of the carrier to the image or poor cleaning.
As described above, any complete device has not been developed as far as the dry type coating device is concerned.
Thus, an object of the present invention is to provide a carrier production apparatus capable of producing the carrier with the ability to form the even resin layer, high yielding rate and high durability.